Living wage is the amount of money required to meet all your needs without government assistance.
“Needs” is the part that has changed. $2k a year in healthcare wasn’t likely included 100 years ago, but most people would consider that a need now.
When I checked the MIT living wage calculator, it listed $600 a month in rent. That’s just barley enough for 1 bedroom apartment with a roommate with 1 person sleeping in the living room.
100 years ago you could likely find some large dormitory style living in a death trap building with inadequate exits. But today short of illegally filling a single family unit with too many people a, single bedroom apartment with a roommate is pretty close to minimum shelter.
“Decent wage” to me implies more than the minimum possible shelter and $9 a day for food. But the point is living wage is an already established term of art that means basically the same thing it always has.